[libre-riscv-dev] [Bug 349] New: privileged-instruction decoding function needed

[libre-riscv-dev] [Bug 349] New: privileged-instruction decoding function needed

[bugzilla-daemon]

https://bugs.libre-soc.org/show_bug.cgi?id=349

            Bug ID: 349
           Summary: privileged-instruction decoding function needed
           Product: Libre-SOC's first SoC
           Version: unspecified
          Hardware: PC
                OS: Mac OS
            Status: CONFIRMED
          Severity: enhancement
          Priority: ---
         Component: Source Code
          Assignee: lkcl@lkcl.net
          Reporter: lkcl@lkcl.net
                CC: libre-riscv-dev@lists.libre-riscv.org
   NLnet milestone: ---

certain operations are privileged.  in the decoder these need to be
marked as such, and a trap raised instead.

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[libre-riscv-dev] [Bug 349] privileged-instruction decoding function needed

[bugzilla-daemon]

https://bugs.libre-soc.org/show_bug.cgi?id=349

--- Comment #1 from Luke Kenneth Casson Leighton <lkcl@lkcl.net> ---
from https://github.com/antonblanchard/microwatt/blob/master/execute1.vhdl

    type privilege_level is (USER, SUPER);
    type op_privilege_array is array(insn_type_t) of privilege_level;
    constant op_privilege: op_privilege_array := (
        OP_ATTN => SUPER,
        OP_MFMSR => SUPER,
        OP_MTMSRD => SUPER,
        OP_RFID => SUPER,
        others => USER
        );

    function instr_is_privileged(op: insn_type_t; insn: std_ulogic_vector(31
downto 0))
        return boolean is
    begin
        if op_privilege(op) = SUPER then
            return true;
        elsif op = OP_MFSPR or op = OP_MTSPR then
            return insn(20) = '1';
        else
            return false;
    end;

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